We're looking at doing some rehab on a hotel.  The exterior walkways appear to consist of composite deck (corrugated steel pans with a 4' slab) with ribs running side-to-side.  Some of the walkways, then, have steel tubes on either side to support the walkway.  But some, instead, have a sheet metal box beam.  These beams have openings in the sides so I can see inside them, thinking they might just be covering a heavier steel member, but there's nothing else there.  These beams span 8' between columns.  I'm wondering if anyone has seen this type of construction and either confirm that the box beams are the primary structural element or if you might direct me where else something could be hidden?  My biggest concern is that some of the box beams are rusted through on the bottom - however, there's no cracking in the slabs nor excessive flexibility.